Vehicle windshield wiper systems often have a depressed park mechanism that reverses the wiper drive motor and rotates the wiper drive post an additional increment when the wiper system is turned off. This lowers the wiper from its normal inwipe position, where it forms a substantial angle with the windshield lower edge, to a park position where it is closer to, and more nearly parallel to, the lower edge. This puts the wiper farther out of view. Usually, there is no obstruction to prevent moving a fixed length wiper down to the park position. However, as windshields become more and more sloped or raked, a wiper that is long enough to Wipe sufficient area of the windshield may be so long that it would hit an obstruction if an attempt were made to park it at its normal, wiping length. This is especially true for the passenger side wiper of a pair of wipers that move back and forth in the familiar tandem pattern. The obstruction may be the side edge molding of the windshield itself, or another vehicle body component such as a hood hinge. Stated differently, there is only a limited space available along the lower windshield edge in which to park the wiper
One proposed solution, disclosed in U.S. Pat. No. 4,780,926 to Kondo et al, is a single, center mounted wiper that is shortened by folding it back on itself jackknife fashion, and which is stowed in a central storage compartment. The wiper is folded by a rack and pinion mechanism that is in turn powered by a motor separate from the wiper drive motor. Another separate motor covers and uncovers the compartment. While the system avoids side edge obstruction, it could not be easily or practically adapted to most existing vehicle body styles. Very few vehicle bodies are designed to incorporate a single wiper. The extra motors represent added complexity, weight and expense. Another drawback is the possibility of the fold-up mechanism failing when the wiper is only partially unfolded. In such a half open position, the wiper would not work as it was swept back and forth, and would be very visually obtrusive.
A much more prevalent wiper system is the two wiper tandem system. A truly practical mechanism for avoiding parking obstruction of the passenger side wipe r would be one that worked in cooperation with such a wiper system without creating a radically different wiper motion or adding a great number of extra components and structure. It would also be a great advantage if the wiper had a fail safe feature, so that it could wipe even if the system failed to fully operate.